Shaft nuts, which are tightened on a thread in the envelope surface of a shaft are used for securing that components fitted to the shaft are maintained in a substantially fixed position. In order to ascertain that the shaft nut is not screwed off unintentionally or as a result of oscillations and movement of the shaft or the component, it has been used locking arrangements incorporating a locking plate, which can be attached to the shaft nut and has an inwardly projecting portion arranged to fit into one of a number of corresponding, axial grooves provided in the shaft. Such an arrangement will prevent unscrewing of the shaft nut. There can only be a limited number of axial grooves in the envelope surface of the shaft and a limited number of apertures in the shaft nut in which the locking plate can be attached, and therefore there is a problem to get the inwardly projecting part of the locking plate register exactly with a groove in the shaft, when the shaft nut has been tightened to a desired position.
U.S. Pat. No. 4,090,545 discloses such a locking plate which has an arcuate body portion having two circular bolt holes for attachment bolts to be screwed into the apertures in the shaft nut. The spacing between the two bolt holes is equal to the distance between two adjacent apertures in the shaft nut. The inwardly projecting portion of this locking plate is offset from the center of the locking plate particularly 4,5°, enabling a larger number of possibilities of alignment between the shaft grooves and the inwardly projecting portion. With this locking plate and locking arrangement it is certainly possible to find tightening positions for the shaft nut, which only require that the shaft nut is turned backwards a few degrees. However, this means that it can not be guaranteed that the locking arrangement according to this patent can provide a positive locking of the shaft nut with an optimal tightness.
DE 203 02 843 U1 discloses another locking arrangement with a locking plate having an inwardly projecting portion arranged to enter in a groove in a shaft, whereby the end of the projecting portion is bent sideways for entering in the shaft groove under the shaft nut. This locking plate is secured to the shaft nut with only one bolt, which extends through an elongated hole in the locking plate and is screwed in into one of the threaded bores in the side face of the shaft nut. The inwardly projecting portion of the locking plate is positioned at one of the ends of the locking plate. The fact that the bolt arresting the locking plate to the shaft nut extends through said elongated hole, means that it is possible to find many positions where the position of the inwardly projecting portion of the locking plate can be brought to coincide with the position for an axial groove in the shaft. The fact that the locking plate is secured with only one bolt, which furthermore is not positively guided by the aperture in the locking plate, means that the strength of the grip between the locking plate and the shaft nut is rather low, which is compensated with an intermediate washer having raised portions, having the effect of cutting itself into the opposed side faces of the locking plate and of the shaft nut. As the end of the inwardly projecting portion is bent like an L, does further mean that the locking plate always must be positioned with the side of the locking plate where the end portion projects in the same direction, which reduces the possibilities of reaching registering positions between projecting end and axial shaft groove.